1. Field of the Invention
The present invention relates to a wavelength tunable demultiplexing filter device, wavelength tunable multiplexing filter device and wavelength routing device which are used for adding and dropping wavelength components (add-drop) in an optical network system so as to demultiplex and multiplex light of arbitrary wavelengths from optical signals.
2. Discussion of the Related Art
With the progress of technologies used for optical wavelength multiplexing division and transmission in optical communication systems, a more versatile and more flexible optical transmission system has been required. In an optical transmission system, light of a desired wavelength must be picked up from an optical signal where wavelengths have been multiplexed at an arbitrary node, or light of a desired wavelength must be added to such optical signals to send them as wavelength domain multiplexed light.
FIG. 1 illustrates the configuration of a conventional four-channel optical add-drop system. In this figure, wavelength-multiplexed light is added to an optical demultiplexing filter device 101 and then the desired wavelengths, for example, xcex1, xcex2, xcex3, and xcex4 are demultiplexed from the multiplexed wavelengths xcex1 through xcexn. Light of the demultiplexed wavelengths goes to optical switches 102a through 102d. Signals of newly modulated wavelengths xcex1 through xcex4 simultaneously enter the optical switches 102a through 102d, respectively. The optical switches 102a through 102d have two input terminals and two output terminals. They select the signals demultiplexed by the optical demultiplexing filter device 101 and the newly modulated signals of xcex1 through xcex4 based on external control signals, and then output them from the two output terminals. The output from each of the optical switches is given to a multiplexing filter device 105 via optical tunable attenuators 103a through 103d and splitting devices 104a through 104d. The splitting devices 104a through 104d extract some of the output from the optical tunable attenuators 103a through 103d and then output it to a monitor 106. The intensities of wavelengths are adjusted at the same level by controlling the output from the optical tunable attenuators via the monitor 106.
For such a conventional optical demultiplexing filter device, the selected wavelengths are previously fixed at xcex1 through xcex4. The number of channels will increase to dozens or several hundred in the near future. This will require multiplexing or demultiplexing light on that number of channels when arbitrary wavelengths are to be selected. For this reason, when an arbitrary channel is selected, all the channels must be temporarily disassembled and then the necessary channel must be selected from them. This causes disadvantages in making the scale of the communication system larger and increasing the transmission losses. At ordinary transmission nodes other than those using optical cross connections in a large-scaled matrix, the ability to select optical signals on several channels is good enough for the purposes of routing, add-drop, and it is desired that arbitrary wavelengths can be selected from a number of channels unlike the conventional fixed wavelengths.
The present invention has been made with attention given to the conventional problems. Accordingly, it is an object of the invention to provide a wavelength tunable demultiplexing filter device, wavelength tunable multiplexing filter device, and wavelength routing device which are used at transmission nodes or the like in a wavelength-multiplexed optical transmission system in order to select arbitrary wavelengths.
The wavelength tunable demultiplexing filter device of the invention demultiplexes arbitrary wavelength components from wavelength-multiplexed light and comprises an optical filter element including a plurality of filter chips arranged thereon which transmit at least one wavelength component of the wavelength-multiplexed light; a light emitting unit which emits the wavelength-multiplexed light into the optical filter element from a specific direction; a first light receiving unit which is located on the same optical axis as the light emitting unit and receives the light transmitted through the optical filter element; a moving unit which moves the optical filter element in a direction that the filter chips are arranged so that the light from the light emitting unit enters another filter chip; and a controller which controls the moving unit in accordance with a wavelength component to be demultiplexed.
The wavelength tunable multiplexing filter device of the invention is used to multiplex wavelength-multiplexed light from which an arbitrary wavelength component is filtered, with the filtered wavelength component, and comprises an optical filter element which has a plurality of filter chips arranged thereon which transmit at least one of wavelength components of the wavelength-multiplexed light; a first light emitting unit which emits light having arbitrary wavelength components of the wavelength-multiplexed light into the optical filter element from a specific direction; a second light emitting unit which emits wavelength-multiplexed light excluding the wavelength components emitted by the first light emitting unit, into a position of the optical filter element, where the transmitted component of the first light emitting unit through the optical filter element is outputted so that light reflected by the filter chip overlaps with the transmitted component of the light from the first light emitting unit; a light receiving unit located on the same optical axis as the first light emitting unit and receives the light outputted from the optical filter element and the light reflected from the second light emitting unit; a moving unit which moves the optical filter element in a direction that the filter chips are arranged to input the light from the first and second light emitting units into different filter chips; and a controller which controls the moving unit in accordance with at least one wavelength component to be multiplexed.
The routing device of the invention is provided with at least one pair of the wavelength tunable demultiplexing filter device and the wavelength tunable multiplexing filter device, and the routing device demultiplexes at least one of wavelength components from wavelength-multiplexed light and multiplexes the same wavelength components as the demultiplexed one with the residual wavelength-multiplexed light.